1 files changed, 5 insertions, 1 deletions

diff --git a/lapi.c b/lapi.c
index 0ca9a321..ae6b07ae 100644
--- a/lapi.c
+++ b/lapi.c
@@ -38,7 +38,11 @@ const char lua_ident[] =
 
 
 
-/* test for a valid index */
+/*
+** Test for a valid index.
+** '!ttisnil(o)' implies 'o != &G(L)->nilvalue', so it is not needed.
+** However, it covers the most common cases in a faster way.
+*/
 #define isvalid(L, o)   (!ttisnil(o) || o != &G(L)->nilvalue)